1. Field of the Invention
The present invention relates to a fastener driving tool for fastening a fastener such as a nail, rivet, or staple to a member to be fastened.
2. Description of the Related Art
In the related art, spring-driven type fastener driving tools employing electric motors are well-known. This type of spring-driven type fastener driving tool uses the drive power of an electric motor to push up a plunger urged by a spring in a direction from a lower dead point to an upper dead point in a fastening direction in resistance to urging force of the spring. The fastener such as a nail is then accelerated in a direction from the upper dead point to the lower dead point by a plunger as a result of the plunger that has been pushed up being released and the fastener is fastened to a member to be fastened.
An electric motor built into a spring-driven type fastener driving tool of the related art drives the plunger from an upper dead point side to an end a position while compressing a spring in resistance to the urging force of the spring using a reduction mechanism provided at a rotation output axis side.
With spring-driven fastener driving tools, in a state of transition after fastening a fastener, the spring is compressed by rotation inertia of a reduction mechanism unit that includes the rotor of a motor and a reduction gear even after a voltage is no longer applied to the electric motor. This means that a mechanism is also required to prevent movement of the plunger in a direction for fastening the fastener as a result of the compressed force of the spring and for preventing movement in the opposite direction to the direction of fastening. Typically, a one-way clutch (reverse rotation prevention mechanism) is provided that prohibits reverse rotation of the rotation output axis of the reduction mechanism unit using urging force (compression force) of the spring when rotation of the motor is stopped.
However, when a spring-driven type fastener driving tool that fastens, for example, larger nails of a length of, for example, 65 millimeters is designed, it is necessary to supply substantial striking power (driving power) to the plunger. It is therefore necessary to make the coil diameter in the spring steel wire diameter of the coil spring large and it is necessary to make urging force (spring force) of the spring with respect to the plunger substantial. However, when the spring force is made large, the drive time taken to move the plunger to the upper dead point becomes substantial. In this event, for example, a time difference occurs between a switch operation time of a trigger switch etc. that permits the firing of a fastening nail and a fastening firing time with a fastener that carries out firing operation that fires a nail every time a nose (push switch) is pressed against a member to be fastened while pulling the trigger switch. This presents a problem that the fastening feeling in response to the fastening switch operation is poor.
In order to resolve this problem, a reduction mechanism unit that reduces high-speed rotation at the motor is connected and a one-way clutch is provided for the reduced rotation output. However, when reverse rotation with respect to the reduction rotation axis is prevented by the urging force of a spring, it is necessary to increase the required allowable torque at the one-way clutch resisting the spring force. This means that a one-way clutch that becomes larger as the spring becomes larger is required. The dimensions and weight of the one-way clutch therefore increase as do the manufacturing costs.
In order to resolve the above situation, it is an object of the present invention to provide a fastener driving tool that can be both small and lightweight because it is not necessary to increase the allowable torque at the one-way clutch.